The present invention relates generally to the art of electric motors, which should be understood as described herein to include generators and other electromechanical machines that effect a conversion between mechanical and electrical power. More particularly, the invention relates to electric motors having protective heaters.
As should be understood by those skilled in this art, electric codes rate motors for use in various environments. For example, the most stringent criteria are reserved for "explosion-proof" motors. Below this level are motors rated for use in "division 2" areas. These motors need not meet the explosion-proof standards, and are therefore less expensive, but are restricted not to exceed a prescribed surface temperature.
Division 2 motors are sometimes exposed to air having a high relative humidity. To prevent condensation on the windings, space heaters have been applied on or within the motor frame, for example as a wrap on the windings or as a cartridge mounted in the frame. The heater may be controlled by the user or may be automatically activated upon deactivation of the motor. In either case, the heater is activated at a period when the motor is at or near its normal operating temperature. It may be possible, therefore, that the additional heat raises the motor's temperature above a maximum desired temperature, for example the temperature rated for a division 2 area.